As is generally known in the art, a torsion beam axle is a kind of suspension system that connects the wheels to the chassis in a vehicle, and includes a plurality of trailing arms that are coupled to the rear (or front) wheels and the chassis, and a torsion beam that connects the trailing arms.
The torsion beam axle has major technical problems in that it must enable good performance of an independent suspension system by implementing a torsion beam having a concurrent torsion characteristic when torsion occurs between the left-hand wheel and the right-hand wheel and simultaneously secure trunk space and price competitiveness, and in that it must make the chassis light by means of an optimized design of the torsion beam.
In the torsion beam axle, the trailing arms are generally made of cast iron in order to improve the supporting force of the left- and right-hand wheels, while the torsion beam is made of steel in order to easily absorb torsion between the left- and right-hand wheels to facilitate elastic torsion deformation during traveling.
At this time, the torsion beam axle must secure sufficient coupling strength between the trailing arms and the torsion beam in the manufacturing process so as to meet load requirements. In this respect, the method of coupling the different materials between the trailing arms and the torsion beam is becoming an important problem.
Conventionally, the coupling method has used fastening elements such as a bolt and nut. However, due to weak coupling strength, the coupling between the trailing arms and the torsion beam has been easy to damage. Friction-welding, in which the trailing arms and the torsion beam are coupled by rotational contact, has been proposed. To this end, expensive equipment has been required, which weakens competitiveness from the aspect of production cost.